Numerous ectoparasiticidal formulations are known in the art and several of these contain synthetic pyrethroids as active ingredients. Most, if not all, of the pyrethroids are known to be very active against a broad field of insects but are also known to exhibit a high degree of irritancy when applied to the skin of an animal. The many patent applications filed in various parts of the world in respect of pyrethroid based pour-on formulations which differ essentially only on their carrier systems bears witness to the search for more appropriate carrier systems.